Indirectly driven low-convergence-ratio implosion experiments are conducted on SGIII prototype laser facility. Neutron yield, ion temperature and bangtime, and also their variation laws with the increase of ablator thickness are measured. These results are analyzed quantitatively and qualitatively, and the difference between the measurements and the calculations is discussed. The degradation of neutron yield is attributed to the hydrodynamic instabilities and implosion asymmetries.